Breast Cancer Types & Subtypes

Breast cancer can be classified into different types and subtypes based on the characteristics of the cancer cells and how they look under a microscope.

Types of Breast Cancer (pathological classification)

Ductal carcinoma (DCIS)

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Non-invasive; starts in the cells that line the breast milk ducts. This type is an early form of breast cancer and is highly treatable. However, if it is untreated or left undetected, it may spread to a more invasive form of breast cancer – this is why early detection through self- breast checks or yearly checkups is critical.

Invasive ductal carcinoma (IDC)

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A common breast cancer that starts in the milk ducts and spreads to other parts of healthy breast tissue.

Lobular carcinoma (LCIS)

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Starts in the lobules (the glands that produce milk) and does not spread into surrounding breast tissue. This type does not always need treatment and uncommonly becomes invasive.

Invasive Lobular carcinoma (ILC)

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The second most common type of breast cancer begins in the lobules. This type can sometimes be difficult to detect early with a mammogram.

Inflammatory breast cancer

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A rare and aggressive type of breast cancer that may not present with a noticeable lump but cause swelling and redness in the breast due to the cancer cells spreading into the skin and lymphatics of the breast. Symptoms of this type may be similar to mastitis: skin redness and swelling, thickening of breast tissue, fever, and breast tenderness. These symptoms generally persist despite the use of oral antibiotics to treat a possible breast infection/mastitis.

Metastatic Breast Cancer (MBC)

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This type of breast cancer is also categorised as Stage 4 and has spread to other body parts, such as the lungs, liver, brain, or bones.

Metastases can happen when:

  • Cancer cells invade into nearby healthy lymph or blood vessels.
  • Cancer cells can migrate to a distant area where it gets lodged and invade the. surrounding healthy tissue. There is a new (smaller) tumour growth at a distant site.

Paget's disease of the breast or nipple (mammary Paget's disease)

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Paget’s disease is a rare type of cancer that affects the skin around the nipple and the areola, causing redness, scaling, and discharge from the nipple. These symptoms may initially be misdiagnosed with other infections or other skin conditions. This tends to present in older women.

Subtypes of Breast Cancer (Molecular subtype classification)

Subtypes are based on the presence of specific proteins, and genes found in the tumour biology.

Hormone receptor-positive (HR+)

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This breast cancer subtype is fuelled by hormones such as estrogen and progesterone. HR+ breast cancer is often treated with hormonal therapy to block the effects of these hormones on the cancer cells.

Breast cancers with these hormone receptors bind to estrogen and/or progesterone which facilitate the proliferation of the cancer cells. 

Estrogen positive (ER+) and progesterone positive (PR+)

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ER+ breast cancers make up about 80% of all breast cancers and have estrogen receptors on the surface of the cancer cells that can attach to the hormone estrogen, while PR+ breast cancer have progesterone receptors on the surface of the cancer cells that can attach to the hormone progesterone. Sometimes, breast cancer cells can have estrogen and progesterone receptors on their surface, referred to as ER+/PR+. Both hormones play a vital role in developing and regulating the female reproductive system, helping maintain bone density, and affecting the skin, brain, and other organs.

The strength of hormone receptor positivity, meaning the number of estrogen or progesterone receptors on the surface of cancer cells, can vary between different breast cancers. All positive results – for either estrogen or progesterone receptors – will be classed as HR+ breast cancers and tend to be more responsive to hormonal therapy, whereas breast cancers that are hormone-receptor-negative with an Allred score of 0 will have little to no effect from hormonal therapy.

The strength of hormone receptor positivity can also affect the prognosis and treatment approach, which is why it’s important for your doctor to test for both hormone receptors after your biopsy to get the most accurate diagnosis and treatment plan.

There are two types of hormone receptor positive breast cancers. Luminal A and Luminal B subtypes.

Luminal A subtype

These are ER positive breast cancers that are low grade, slow growing and generally strongly ER and PR receptor positive. These cancers are not very aggressive and carry a good prognosis with complete treatment including endocrine treatment (hormone blocking drugs).

Luminal B subtype

These are ER positive breast cancers that can be high grade, can grow more rapidly and are generally PR receptor weakly positive or negative. These cancers are often treated with chemotherapy and endocrine treatment.


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HER2-positive breast cancers

These cancers test positive for a protein called human epidermal growth factor receptor 2 (HER2). This protein promotes the growth of cancer cells. HER2-positive breast cancers tend to be more aggressive than other types of breast cancer.

With treatments including chemotherapy and targeted therapy that now specifically target HER2, the prognosis is good.

HER2-positive breast cancers can be triple positive where ER and PR receptors are also positive in which case endocrine treatment (hormone blocking drugs) are often used. 

Triple-negative breast cancer (TNBC)

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TNBCs are breast cancers that are not ER, PR or HER2 positive. They can be aggressive with sometimes a higher chance of recurrence after initial treatment. They can be fast-growing and therefore often first diagnosed when it has reached the later stages.

This subtype is characterised by the absence of the three main proteins that drive most types of breast cancer (HER2, estrogen receptors, and progesterone receptors). Triple-negative breast cancers do not respond to hormonal or targeted therapies. They are often treated with chemotherapy. Younger women with this subtype may have a genetic predisposition for their cancer but not always.

With many ongoing breast cancer trials and new drugs available, TNBCs are now also being treated effectively with a combination of chemotherapy and other systemic drugs.